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eppramod

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Poly Resistor Current density/Power density Guidelines
Jul 23^rd, 2008, 5:05am

Experts,

Don't know if this topic was discussed here.
I would like to know while sizing Poly resistors (silicided/or unsalicided)
what should be the critical parameter W or L in terms of reliability?

To be more specific i read somewhere that resistor degradation mechanism in lower technologies is more due to Joule (self) heating
rather than Current induced EM (Jmax limits).
So people fix min W for Current density (Jmax) limits and people may have to think min L for Power density reasons.Even very low Jmax
values can raise the local temperature considerably?

Please give your thoughts

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vivkr Community Fellow Offline Posts: 780	Re: Poly Resistor Current density/Power density Guidelines Reply #1 - Jul 23^rd, 2008, 11:39pm Hi, The sheet resistance of poly is fixed and so is the max. current density. If you are trying to realize a particular value of resistance at a certain current density, then you only have the choice of varying W. L is automatically determined. Regards Vivek
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eppramod

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Re: Poly Resistor Current density/Power density Guidelines
Reply #2 - Jul 24^th, 2008, 10:52pm

Hi Vivek,

I understand that point the rho or Jmax values are fixed in a particular technology for poly resistors and you may fix mostly W(or L?) and Come up with a L (or W)for realising particular resistance.

But this fixing W (or L?) minimum value can be (will be) determined by Jmax limits.But what i came across was this minimum W or L is now determined by Power density more than Current density.
I wanted to know if this is true.

Thanks for your response

Pramod

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vivkr Community Fellow Offline Posts: 780	Re: Poly Resistor Current density/Power density Guidelines Reply #3 - Jul 24^th, 2008, 10:55pm Hi Pramod, They are the same thing. Since sheet resistivity is a process constant, a fixed power density corresponds to a fixed current density. Regards Vivek
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wave Senior Member Offline Posts: 117 Silicon Valley	Re: Poly Resistor Current density/Power density Guidelines Reply #4 - Dec 29^th, 2008, 8:41pm I've actually found that for small Poly R's with high currents (several mA), I need to watch the # of contacts the layout tool puts on the end. A default of 2 contacts may be a large % of effective resistance AND not meet current density guidelines. ~WAVE
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Maks

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Re: Poly Resistor Current density/Power density Guidelines
Reply #5 - Jan 23^rd, 2009, 12:32pm

wave wrote on Dec 29^th, 2008, 8:41pm:

I've actually found that for small Poly R's with high currents (several mA), I need to watch the # of contacts the layout tool puts on the end.

A default of 2 contacts may be a large % of effective resistance AND not meet current density guidelines.

~WAVE Cool

You may have to watch not only the number of the contacts, but their layout as well - the edge and especially corner contacts/vias in the contact/via array may carry much higher current than the average current...

Maks
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